The invention relates to a crenellated stepped end-gauge block arrangement of the type having an elongate supporting body and a plurality of end-gauge blocks secured thereto along a straight line at defined distances from one another. For example, such a gauge-block arrangement is disclosed in the German periodical "VDI-Z", 1980, page 535 et seq., in particular page 542 and FIG. 14.
The above-noted literature reference contains a description of the use of stepped end-gauges, of this type, for checking the accuracy of multi-coordinate metrology equipment, it being possible to install these stepped end-gauges, within the measuring volume of the metrology equipment, horizontally, vertically, or at an inclination in space.
In the case of the crenellated, stepped end-gauge shown in the above-mentioned publication, short, individual end-gauge blocks, having a length of for example, 10 mm, are assembled in a row, in a staggered arrangement which produces a crenellated profile. The end-gauge blocks are, if necessary, bolted together. The resulting row of end-gauge blocks, which contains no gaps, is inserted into a supporting body as a complete unit. The row of end-gauge blocks possesses a crenellated profile both on its upper surface and on its lower surface, and it is inset into a comparatively deep elongate recess in the supporting body, which is large, overall, in the vertical direction, only every second end-gauge block projecting from the top of the supporting body, in the manner of crenellations. In this design, the end-gauge blocks are in continuous contact with one another, or are wrung against one another, as the case may be. In the course of use with such contact, long-duration processes occur in the contact zone, such as for example, the expansion of oil, molecular welding, chemical corrosion, and the like, having an unknown influence and leading to very slow changes in the dimensions of the stepped end-gauge. In addition, the bedding-in into the supporting body of the row of end-gauge blocks can cause further unknown changes in deformation and/or in length.
The known stepped end-gauge blocks are located very far from the neutral bending axis or fiber of the supporting body, and accordingly experience a comparatively large change in length as a result of the sagging of the stepped end-gauge under its own weight, depending on its attitude in space, the manner in which it is clamped in position, and its state of flexure and/or as a result of deformations due to external forces (clamping forces, touching forces, etc.). When the stepped end-gauge is heated, the effective coefficient of expansion is indefinite, because the end-gauge blocks, which for their part, are made of steel, and the supporting body made of grey cast iron, possess different coefficients of expansion under any given conditions. These dissimilar expansions can result in temperature-dependent curvature, in the manner of a bimetallic strip. Since end-gauge blocks are manufactured only in exact decimal lengths, only corresponding spacings can be achieved in the case of this type of stepped end-gauge. As a result of unavoidable, albeit small tilting and/or convexity of the opposing contact surfaces within the uninterrupted row of end-gauge blocks, corresponding errors can accummulate so that it is impossible to guarantee adequate parallelism of the surfaces which are touched within the crenellated stepped end-gauge at every point, in the case of every stepped end-gauge, and/or at every point in time. The last-mentioned possibility of error can be avoided, or minimized, only by carrying out a series of very precise initial measurements, and by a compensating assemblage of different end-gauge blocks possessing errors of the same nature, but the other disadvantages remain unaffected.
In the past, stepped end-gauges have even been machined, with crenellations from the solid, in which the touchable surfaces on the one hand, and the supporting body on the other hand, are composed of the same material, and constitute a homogeneous workpiece. Although this type of crenellated stepped end-gauge avoids many of the above-mentioned disadvantages, it is nevertheless unavoidable, even in the case of this type of stepped end-gauge, that the tops of the crenellations lie outside the neutral bending axis, and the distances between the surfaces which are to be touched consequently vary as a result of the sagging of the stepped end-gauge under its own weight and under the action of external forces. Since, when being machined from the solid, the workpiece is comparatively large, it is thus impossible to produce the surfaces which are to be touched to such a high quality and parallelism as in the case of comparatively small end-gauge blocks. In the case of large stepped end-gauges, it is difficult, or even impossible to harden the entire body, or even to harden only the surfaces which are to be touched. Superfinishing the numerous surfaces to be touched by lapping, is likewise beset with difficulties.
In addition to these crenellated stepped end-gauges, staircase-like stepped end-gauges have also previously been assemblied from end-gauge blocks of different lengths which were clamped, as a group, on a supporting base body (compare, in addition to the literature reference already mentioned in the introduction, also "VDI-Berichte", No. 378, 1980, page 21 et seq.), but the surfaces of a stepped end-gauge of this type which are to be touched possess no common measurement axis.
An object of the invention is to provide a crenellated stepped end-gauge which avoids the above-mentioned disadvantages, and which thus undergoes no uncontrolled changes which affect the distances between the surfaces which are to be touched.
This object is achieved according to the invention by providing the end-gauge block supporting surfaces of the supporting block at a longitudinally extending groove in the supporting body, in which groove the end-gauge blocks are disposed and individually secured, one behind the other, on the flanks of this groove. Preferably the end-gauge blocks are designed in the form of cylinders with axes extending parallel to the longitudinal extent of the groove. By virtue of the separate installation of the various end-gauge blocks in a groove, which is preferably V-shaped, no effects can result from uncontrolled long-term processes in the contact zone between end-gauge blocks which are wrung or pressed against one another, because an interspace is always present between adjacent end-gauge blocks, and contact zones of the above-mentioned nature are avoided. The coefficient of expansion of the supporting body is now the factor which uniquely determines the unavoidable, temperature-dependent dimensional changes of the stepped end-gauge, for which supporting body it is possible to select a material which appears suitable, for example steel, aluminum, granite, or invar, without being limited in any way to coefficients of expansion, or similar parameters. On the supporting body, it is merely necessary that the flanks be accurately machined in the region of the bottom of the V-shaped groove, less accurate machining sufficing for the other surfaces of the supporting body, which requires no hardening treatment. The small end-gauge blocks, which are inserted permanently, can be hardened and precision-finished without difficulty, thereby enhancing their wear-resistance, accuracy of shape, and surface quality.
By virtue of the fact that the longitudinal positions of the individual end-gauge blocks can be arranged at will, it is also possible to produce very "crooked" dimensions on the stepped end-gauge. The orientation of the end-gauge blocks, in the supporting body is definitely fixed by reason of the groove. The maximum deviation from the ideal shape results merely from the errors in the accurately machined groove and, in each case, the individual error affecting one end-gauge block. No accummulation of geometrical errors occurs within a comparatively long row of end-gauge blocks.
The cross-section of the supporting body is designed in a manner such that the central axes of the end-gauge blocks, which are placed in the bottom of the groove, are located within the neutral bending axis or fiber of the supporting body. As a result, length changes due to deformations of the stepped end-gauge, under its own weight and/or under the action of external forces, are avoided, only very small and for the most part, negligible angular changes affecting the surfaces which are to be touched being still possible. Since, therefore, sagging has no appreciable influence on the distance between the surfaces which are to be touched, the cross-section of the supporting body can be designed to be both light and small, which renders the stepped end-gauge easier to handle. Due to the fact that the V-shaped groove is deep, the end-gauge blocks are located in a manner in which they are protected, while at the same time they are freely accessible within a widely diverging angular space. As a result, lateral clamping of the stepped end-gauge is also possible.
In addition to plane-parallel end-faces, spherically domed surfaces or conical shapes can also be considered for the preferably cylindrical end-gauge blocks, which end-faces are for the most part the faces which are to be touched.
Further objects, features, and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, several embodiments in accordance with the present invention.